Eletrical recordings will be made from single neurons from different parts of the hippocampal formation (Ammon's horn, dentate gyrus, subiculum, presubiculum, postsubiculum, parasubiculum, medial and lateral entorhinal cortex and perirhinal cortex) in freely moving rats quantitatively analyzed with a TV-computer based system. In the tasks whichl will be used, neurons from some of these regions are known to fire when the rat is at a specific location or when the rat's head is pointing a specific direction, or some combination of location and direction, i.e., to signal information necessary for some kinds of navigation. From what is known already, the flow and transformation of navigational information can be partially sketched out. By recording from more regions, this flow and transformation should become much clearer. A new task will be introduced in which rats will move between two different environments. This task is designed to especially test the control of head directional firing across environments. Almost nothing is known about the neuronal mechanisms of navigation. The ability to navigate is often lost in dementia, and is an especially serious deficit because the people get lost. Navigation is complex non verbal cognition, and the problem of cellular analysis of flow and transformation of representations in this cognitive process seems solvable.